The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.
The present invention relates generally to lasers and more specifically to a design for a phonon-pumped laser system. Ever since the invention of the laser, electrical pumping and optical pumping have been the primary laser pumping methods. To the best of our knowledge, no one has proposed to pump a laser solely with phononsxe2x80x94an alternative that is potentially important and practical. This invention presents the first conception and analysis of a phonon-pumped semiconductor laser designed for far-infrared THz emission.
Photon pumped lasers are known and described in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 4,592,056, May 27, 1986, Resonant photon pumping mechanisms for a plasma x-ray laser, Elton, Raymond C., and
U.S. Pat. No. 4,398,294, Aug. 9, 1983, High power nuclear photon pumped laser, Miller Thomas G.
However the xe2x80x9cphononxe2x80x9d is defined as the quantum of crystal lattice vibrational energy. Phonons are analogous to the quanta of light, i.e. photons.
Phonon based lasers are shown in U.S. Pat. No. 5,699,372, Dec. 16, 1997, Wavelength-conversion solid-state laser, Okazaki, which uses a semiconductor laser as a pump source; and U.S. Pat. No. 3,624,553, Nov. 30, 1971, Cyclotron resonator laser in a P-type semiconductor, Van-Tran, Nguyen.
The invention is a miniature, cw, semiconductor superlattice laser whose wavelength of emission is in the 30 to 120 um range. No optical pumping or electrical pumping is used. There are no electrical contacts on the superlattice which is in the flat-band condition. The coherently strained superlattice is epitaxially grown from IV-IV or III-V or II-VI materials. The dispersion curves of the superlattice as a function of superlattice wavevector kZ are engineered by choice of quantum well-and-barrier composition and thickness to create a four-level laser system for the two minibands of interest: either conduction minibands, or valence minibands. The quantum wells are doped n-type (for CB lasers) or p-type (for VB lasers), and LO optical phonons are used to pump carriers from the populated ground state miniband valley to the laser""s upper miniband. The LO phonons have a higher effective temperature than acoustic phonons present in the superlattice because a semiconductor xe2x80x9cheat buffer layerxe2x80x9d atop the superlattice (transparent to acoustic phonons) is used to reflect LO phonons back into the laser and confine them there. The vertical radiative THz emmision is between minibands. The hot LO phonons are created by a temperature gradient across the superlattice. A cold sink (Txcx9c77K) contacts the lower surface of the superlattice and a hot sink (Txcx9c300K) contacts the top surface. A cold finger may be the lower sink, and a thin-film electrical-resistance-heater may be the upper heat sink. The laser may also be constructed by engineering an opposite curvature for dispersion curves as a function of inplane wavevector kX or kY, an engineering of inverted effective mass.